FIG. 1 is a schematic view of the structure of a cellular wireless communication system. As shown in FIG. 1, the cellular wireless communication system mainly consists of terminals, an access network and a core network. The network, consisting of eNBs or eNBs and base station controllers, is called a Radio Access Network (RAN). The RAN is responsible for access stratum transactions, such as radio resource management. Physical or logical connection could exist between eNBs based on the actual situation, such as between eNB 1 and eNB 2 or between eNB 1 and eNB 3 as shown in FIG. 1. Each eNB could be connected with one or more core network (CN) nodes. The CN, responsible for non-access stratum (NAS) transactions like location update, is also an anchor point of user plane. User Equipment (UE) refers to various types of equipment that could have communication with the cellular wireless communication system, such as mobile phones or laptops.
In the cellular wireless communication system, the wireless coverage of a fixed eNB network is restricted for all sorts of reasons, such as inevitable coverage holes in radio network due to the obstruction of building structures to radio signals. On the other hand, in cell-edge areas, due to the attenuation of radio signals and interference from the neighbor cells, the communication quality of a UE in the cell-edge areas is poor and the error rate of wireless transmission rises. To raise the coverage of data rate, group mobility, temporary network deployment, throughput in the cell-edge areas and coverage in a new region, a solution is to introduce a radio network node in the cellular wireless communication system. The introduced node is called Relay.
In Relay, there is a kind of station having the function of relaying data and probable control information among other network nodes through a radio link, and this station is also called Relay Node/Relay Station. FIG. 2 is a schematic view of relay network architecture. As shown in FIG. 2, the UE directly served by eNB is called Macro UE, and the UE served by a Relay is called Relay UE. A Direct link is the radio link between an eNB and a UE, comprising downlink/uplink (DL/UL) direct link; an access link is the radio link between a Relay and a UE, comprising DL/UL access link; and a backhaul link is the radio link between an eNB and a Relay, comprising DL/UL relay link.
Relays could relay data through several methods, such as directly amplifying radio signals received from eNBs, or correspondingly processing the data received from eNBs and then forwarding the correctly received packages to UEs, or eNBs cooperating with Relays to send data to UEs. Relays could also relay data from UEs to eNBs.
Among many Relay types, a kind Relay, called Type I relay, has characteristics as follows.
A UE can not distinguish a Relay from a cell under a fixed eNB, namely, from the point of view of a UE, the Relay itself is just a cell and has no difference from a cell under an eNB, and this kind of cell is called a Relay cell. The relay cell has its own physical cell identity (PCI), and broadcasts just like a common cell. When a UE resides in the Relay cell, the Relay cell could separately distribute and dispatch radio resources for the UE, independent from the radio resource dispatching of an eNB participating in relay. The eNB participating in relay is also called Donor eNB, which is the eNB connected to a Relay by a backhaul link. The interface and the protocol stack between a Relay cell and a Relay UE are the same as that between a common eNB cell and a UE.
Type I Relay is called Relay Node (RN). The eNB responsible for Type I Relay access is called Donor-eNB (DeNB). The air interface between RN and Relay UE is called Uu interface. The air interface between RN and DeNB is called Un interface, wherein, on the Uu interface, all wireless access layer control plane and user plane protocols terminate in RN; on the Un interface, at least the protocol layers of Wireless Media Access Control Protocol (MAC), Radio Link Control Protocol (RLC) and a protocol for header compression and decompression (Packet Data Convergence Protocol, PDCP) are included.
An LTE system adopts an Internet Protocol (IP)-based flat network. FIG. 3 is a schematic view of LTE network architecture. As shown in FIG. 3, the LTE network consists of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and CN nodes, wherein a CN node comprises a Mobility Management Entity (MME), a Serving Gateway (S-GW) and other support nodes. The MME is responsible for control plane works, such as mobility management, processing of NAS signaling, and management of mobility management context of a user. The S-GW is responsible for the transmission, forwarding and route switching of UE user plane data. The eNBs are logically connected with each other though X2 interfaces, adopted to support the mobility of UE in the whole network and to guarantee users' seamless handover. Each eNB is connected to the core network through an S1 interface and System Architecture Evolution (SAE), which means that the eNB is connected with an MME through an S1-MME interface of a control plane, and is connected with an S-GW through an S1-U interface of a user plane, wherein the S1 interface supports multipoint connection between eNB and MME/S-GW.
FIG. 4 is a schematic view of a protocol stack of an X2-control plane interface. As shown in FIG. 4, the network layer thereof adopts the IP protocol, the transport layer above the network layer adopts the SCTP protocol, and the application layer on the top (namely the control plane) adopts the S1-AP protocol, the transmission carrier at the bottom layer is adopted for sending the S1-AP signaling. FIG. 5 is a schematic view of a protocol stack of an S1-user plane interface. As shown in FIG. 5, in the protocol stack of the S1-U interface, GTP-U/UDP/IP forms a transmission carrier which is adopted to send user plane Protocol Data Unit (PDU) between the eNB and the S-GW. The transmission carrier is identified by TEID of GTP-U and IP address, comprising: GTP-U TEID (Tunnel Endpoint Identifier) at source side, GTP-U TEID at target side, IP address at source side and IP address at target side, wherein the UDP port number is fixed to be 2152, and GTP-U is a tunneling protocol adopted to achieve seamless transmission on IPv4 and IPv6. Each transmission carrier is adopted to carry the service data flows of one service.
Each eNB performs signaling and data transmission with a UE through the Uu interface (initially defined as a wireless interface between the UTRAN and the UE). FIG. 6 and FIG. 7 show the air interface protocol stack between eNB and L1, L2 and L3 of UE from control plane and user plane respectively.
Before the network element of RN is introduced, there has been clear definition of X2 interface by LTE-A system in the prior art: the X2-AP protocol terminates at the RN. FIG. 8 is a protocol stack of the X2 interface of a control plane supporting RN. As shown in FIG. 8, there is only one X2 interface link between a RN and a DeNB, and there is only one X2 interface link between a DeNB and other eNB with an X2 interface relationship. The DeNB processes and forwards all the UE-dedicated processes between an RN and other eNBs. Non-UE-dedicated processes are only processed between RNs and DeNBs or between DeNBs and other eNBs.
FIG. 9 is a schematic view of typical network architecture after the introduction of an RN network element. As shown in FIG. 9, RN equipment is connected to the DeNB, and X2 interface links exist between DeNB and RN and between DeNB and eNB. After the UE accesses the RN equipment, the UE could switch to other network elements, for example, it could switch to DeNB, eNB through S1 interface or X2 interface respectively.
Between RN and the eNB network element there might be a situation of neighbor cells existed, a UE on the RN could switch to the eNB. This requires that the RN needs to obtain necessary information of the eNB so as to support the realization of a switch function between the RN and the eNB, wherein the information comprises GU Group Id List information, which indicates a pool of the core network that the eNB belongs to, and is adopted for the network element to judge whether the switching type is S1 switching or X2 switching. If the network element finds that the pool of the core network it belongs to is different from that in the target side, the network element has to choose the S1 switching; moreover, if the network element does not have this information, the network element has to choose the S1 switching.
The corresponding relationship, established on the network element, between the eNB identifier (eNB id) and the GU Group Id List of the pool of the core network thereof is a necessary support for judging the switching function. But in the system with the introduction of the RN, such corresponding relationship could not be established through the existing technology yet, especially between the RN network element and the eNB network element.
In the public known technologies, the sending of X2 interface information between an RN and an eNB could be performed by the following methods.
Consider the sending of interface information of the eNB to the RN. If there exists an X2 interface in the eNB and the DeNB, the eNB could adopt an eNB configuration update process or an X2 setup process of the X2 interface protocol to send the network element information to the DeNB through the X2 interface between the eNB and the DeNB, wherein the eNB network element information is sent as a serving cell of the eNB to DeNB. The DeNB could adopt an eNB configuration update process or an X2 setup process of the X2 interface protocol to send the eNB network element information to the RN through the X2 interface between the DeNB and the RN, wherein the eNB network element information is sent as a serving cell of the DeNB to the RN.
On the other hand, consider how RN interface information is sent to the eNB. The RN could adopt an eNB configuration update process or an X2 setup process of the X2 interface protocol to send the RN network element information to the DeNB through the X2 interface between the RN and the DeNB, wherein the RN network element information is sent as a serving cell of the RN to the DeNB. If there exists an X2 interface in the eNB and the DeNB, the DeNB could adopt an eNB configuration update process or an X2 setup process of the X2 interface protocol to send the RN network element information to the eNB through the X2 interface between the DeNB and the eNB, wherein the RN network element information is sent as a serving cell of the DeNB to the DeNB.
However, during the process above, for example, when the DeNB forwards the eNB network element information to the RN, if the eNB is just treated as the serving cell of the DeNB to be sent to the RN, the DeNB could only send the serving cell information sent by the eNB to the RN, but the GU group Id list of the eNB could not be added in the GU group Id list of the DeNB for sending, thus the RN would get a wrong corresponding relationship between the eNB id and the GU Group Id List, therefore the fundamental functions, such as judgment on a switching type, can not be fulfilled.